Key Derivation Function

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Pronunciation

[kee der-uh-vey-shuhn fuhngk-shuhn]

Analogy

Imagine you have one master key (a password or a main secret). A Key Derivation Function is like a sophisticated machine that takes this master key and, through a complex and lengthy process (often involving mixing it with other non-secret ingredients like a ), produces one or more new, stronger, and purpose-specific keys. It's like turning a simple password into a set of highly secure cryptographic keys.

Definition

A cryptographic algorithm that derives one or more secret keys from a master key or a password using a pseudorandom function. KDFs are often used to stretch keys, making them more resistant to brute-force attacks, or to generate multiple keys from a single source.

Key Points Intro

KDFs transform input secrets into cryptographically suitable keys.

Key Points

Derives cryptographic keys from a secret value (e.g., password, master key).

Often incorporates a salt to protect against precomputation attacks (e.g., rainbow tables).

Can be designed to be computationally intensive (key stretching) to slow down brute-force attacks on the input secret.

Used in password storage, disk encryption, and generating keys for various cryptographic protocols.

Example

When you set a password for an encrypted file archive, a like or is used to take your relatively weak password, combine it with a random , and perform thousands of computations to derive a strong cryptographic key that is then used to encrypt the file.

Technical Deep Dive

KDFs are typically built from cryptographic primitives like functions (e.g., ) or ciphers. An important property of many KDFs, especially those used for passwords, is 'key stretching' or 'work factor'. This means they are deliberately slow, requiring significant computational effort to produce the derived key. If an attacker tries to guess passwords, they must perform this computationally expensive operation for each guess, making brute-force attacks much slower and less feasible. Parameters like the iteration count (for , ) or memory usage (for , Argon2) control this work factor.

Security Warning

The security of a depends on the strength of the input secret, the choice of algorithm, its parameters (like iteration count and ), and the underlying cryptographic primitives. Using a weak password with even a strong will result in a weak derived key.

Related Terms

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